<p>Currently, both biochar and nickel additions have been shown to improve the inhibition of anaerobic digestion by high salinity organic wastewaters (HSOWs). Nickel (Ni) plays an important role in the growth of methane producing archaea and enzyme synthesis. This study evaluated the effects of different types and dosages of nickel-loaded biochar (biochar/Ni) on methanogenesis under high salinity conditions. Crayfish shells, pine sawdust, and sewage sludge were pyrolyzed at 600&#xa0;°C to generate biochar/Ni. The results indicated that biochar/Ni could enhance methane production in batch anaerobic digestion experiments, similar to the hormone supplementation effects of “low concentration promotion and high concentration inhibition”. In particular, nickel-loaded sewage sludge biochar (SSBC-Ni) with 13.3 g/L increased the specific methanogenic activity (SMA) by 55.05%, the coenzyme F₄₂₀ content by 70.54%, and cumulative methane production by 10.86% from the control group&#xa0;(without biochar/Ni). The excessive dosage (20 g/L) of nickel-loaded crayfish shells biochar (CBC-Ni) significantly caused the suppression of the above process. In addition, biochar/Ni affected the chemical morphology distribution and bioavailability of Ni in sludge, especially the organic/sulfide fraction of Ni. The results of morphology distribution showed that the addition of SSBC-Ni could increase the water-soluble and exchangeable components of Ni in sludge, and improve the bioavailability of Ni. The high proportion of residual fraction of nickel (69.33 ± 4.44% and 62.76 ± 3.76%) with high CBC-Ni doses, may affect process performance by hindering Ni bioavailability and methane generation. This study proposed the potential enhancement of biochar/Ni on anaerobic digestion of HSOWs.</p> Graphical Abstract <p></p>